[Insight-users] Optimal sigma values for DoG in HoughTransform2DCirclesImageFilter

[Gunderson, Keith R]

Hello,

I do not understand how to determine what sigma value is best for my
application.  Are there any on-line resources that describe this apsect
of the DoG function or should I hit the old textbook again?

Here are the details...  I'm segmenting cylindrical regions of material
from CT images of a phantom.  The regions are a few different radii (
6mm, 15mm) and different density/pixel intensity.  My pipeline looks
like this:

Reader -> CastImage -> ExtractImageFilter ->
MinimumProjectionImageFilter -> IntensityWindowingImageFilter
->  InvertIntensityImageFilter(optional) -> HoughTransformFilterType


I've pretty tightly defined the radius:
  houghFilter->SetMinimumRadius(  (_radius - 1 ) / spacing[0]);
//spacing is ~0.5mm
  houghFilter->SetMaximumRadius(  (_radius + 1 ) / spacing[0]);

I'm having decent success with:
  houghFilter->SetSweepAngle( 6 );



The tool found the center of most of the cylinders/ circles pretty
accurately with sigma = 2.0.  A few of the circles were not found
accurately though.  Through trial and error I found that increasing
sigma generally increased the accuracy in these cases until a sigma=10.0
produced an accurate center result.

Why is this so?  Does a increased sigma always tend to increase the
accuracy (perhaps with a decrease in speed)?  Or should sigma be related
to the radius or intensity range in the circle?

Thanks much,
 
Keith Gunderson

Physiologic Imaging

UIHC, Department of Radiology

200 Hawkins Drive, CC-713 GH

Iowa City, Iowa 52242-1077

Tel: 319-356-1407

Fax: 319-356-1503

Email: Keith-Gunderson at uiowa.edu <mailto:Keith-Gunderson at uiowa.edu> 



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